Example Questions

Example Question #1 : Other Intermolecular Forces

Which intermolecular force would be the result of a polar molecule generating a dipole in a nearby nonpolar molecule?

Possible Answers:

Hydrogen bonding

Ion-dipole

London dispersion force

Dipole-induced dipole

Dipole-dipole

Correct answer:

Dipole-induced dipole

Explanation:

A polar molecule has both positive and negative ends. This dipole can interact in many ways with other molecules, both polar and non-polar. If it interacts with a neighboring nonpolar molecule, there is an induced dipole within that neighbor resulting in a dipole-induced dipole force.

Biomolecules contain carbon as their key element, and they mostly contain nonmetallic elements. For example, the human body is about 65% oxygen, 20% carbon, 10% hydrogen, and 3% nitrogen - the remaining major elements that make up the human body are calcium, phosphorous, magnesium, sulfur, potassium, sodium, chlorine, and other trace elements like iron and copper. Ionic bonds are rare in biomolecules, as most biomolecules are bound via covalent bonds. Also, to create a specific biomolecule, many of the bonds must be in specific orientations-specific stereoisomers are important, especially with enzymes.

Example Question #23 : Fundamental Macromolecules And Concepts

Which molecule has polar bonds but is not itself polar?

Possible Answers:

Correct answer:

Explanation:

In , each bond is polar, as oxygen is much more electronegative than carbon. However, these dipole moments are equal in charge and this molecule is linear with carbon in the middle, so the entire molecule is nonpolar.

In water, oxygen is more electronegative than hydrogen; thus, electrons are pulled toward the oxygen atoms more than towards hydrogen atoms. This gives oxygen a partial negative charge and hydrogen a partial positive charge. The entire molecule is polar since water's molecular geometry is bent.

Methane includes a carbon with a hydrogen attached to each of its four bonds. Electrons are distributed relatively equally across each bond since the electronegativities of hydrogen and carbon are comparable, and the entire molecule is tetrahedral. Thus, neither the individual bonds nor the entire molecule are polar.

In , nitrogen is left with a lone pair of electrons after it bonds with three hydrogen atoms. Because of this lone pair, the molecular geometry is trigonal pyramidal and the entire molecule is polar with the nitrogen atom being slightly negative (high electronegativity) and the hydrogen atoms being slightly positive.

Example Question #21 : Fundamental Macromolecules And Concepts

Once inside a potassium channel, a ions sheds the water molecules surrounding it in order to continue through. How is the ion now stabilized within the channel?

Possible Answers:

An amino acid stretch with negative charges

An amino acid stretch capable of forming hydrogen bonds with the ion

An amino acid stretch capable of forming ionic bonds with the ion

An amino acid stretch with positive charges

An amino acid stretch with neutral charges

Correct answer:

An amino acid stretch with negative charges

Explanation:

Free floating is surrounded by water molecules which stabilize its positive charge. However, once these water molecules are shed due to movement through the potassium channel, something else must stabilize the positively charged ion. This is accomplished via an amino acid stretch with negatively charged residues. The amino acid stretch responsible for the stabilization is Thr-Val-Gly-Tyr-Gly.

Example Question #26 : Fundamental Macromolecules And Concepts

While certain bonds within a polypeptide chain are able to rotate, the actual conformations found in nature are limited. What is a major factor limiting the available conformations?

Possible Answers:

Steric clashes between side chains in a trans conformation.

Hydrophobic interactions between side chains in a trans conformation.

Steric clashes between side chains in a cis conformation.

Steric clashes between backbones in a cis conformation.

Hydrophobic interactions between side chains in a cis conformation.

Correct answer:

Steric clashes between side chains in a cis conformation.

Explanation:

While the peptide bond in a polypeptide chain is locked and unable to rotate, the amino nitrogen-alpha carbon bond can rotate. Additionally, the alpha carbon-carboxyl carbon can rotate as well.

However, like in many other molecules, the cis conformation is energetically unfavorable due to steric hindrance. This steric hindrance occurs when the side chains of two residues are right next to each other within the polypeptide. This is unfavorable, and the trans conformation is therefore preferred.

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